To anyone who knows what they are doing, both pi and tau are simply constants. Absorb either into some constant term, or carry it around with you wherever you go---it doesn't matter. Real engineers, mathematicians, scientists, etc can handle either constant without difficulty. The real advantage that tau has over pi is pedagogical. It is much easier to communicate the relation between angle measure and arc length with tau. Since trig functions deal with lengths more readily than area, it makes sense to teach people trigonometry using a constant that is more closely related to length.